ENH: unify use of dictionary method names

- previously introduced `getOrDefault` as a dictionary _get_ method,
  now complete the transition and use it everywhere instead of
  `lookupOrDefault`. This avoids mixed usage of the two methods that
  are identical in behaviour, makes for shorter names, and promotes
  the distinction between "lookup" access (ie, return a token stream,
  locate and return an entry) and "get" access (ie, the above with
  conversion to concrete types such as scalar, label etc).

etc/codeTemplates/functionObject/FUNCTIONOBJECT.C

@@ -52,7 +52,7 @@ Foam::functionObjects::FUNCTIONOBJECT::FUNCTIONOBJECT
 )
 :
     fvMeshFunctionObject(name, runTime, dict),
-    wordData_(dict.lookupOrDefault<word>("wordData", "defaultWord")),
+    wordData_(dict.getOrDefault<word>("wordData", "defaultWord")),
     scalarData_(dict.get<scalar>("scalarData")),
     labelData_(dict.get<label>("labelData"))
 {